17 with parental consent, 18 for voluntary service. Maximum age for first-time enlistment is 35 for the Army,[1] 28 for the Marine Corps, 34 for the Navy, 39 for the Air Force,[2] and 27 for the Coast Guard.[3]

The U.S. Armed Forces is one of the largest militaries in terms of number of personnel. It draws its personnel from a large pool of paid "volunteers; although "conscription has been used in the past in various times of both war and peace, it has not been used since 1972, but the "Selective Service System has 17 million males on record with the "Selective Service.[9] As of 2016, the U.S. spends about $580.3 billion annually to fund its military forces and "Overseas Contingency Operations.[4] Put together, the U.S. constitutes roughly "40 percent of the world's military expenditures. For the period 2010–14, the "Stockholm International Peace Research Institute (SIPRI) found that the U.S. was the world's largest exporter of major arms, accounting for 31 percent of global shares. The U.S. was also the world's eighth largest importer of major weapons for the same period.[10] The U.S. Armed Forces has significant capabilities in both defense and "power projection due to its large budget, resulting in advanced and powerful equipment, and its widespread deployment of force around the world, including about 800 military bases in foreign locations.[11] Added to this, the largest air force in the world is the U.S. Air Force. Moreover, the world’s second largest air arm is the U.S. Navy and the U.S. Marine Corps combined.[12] The "U.S. Navy is the largest "navy by "tonnage.[13]

Command over the U.S. Armed Forces is established in the "United States Constitution. The sole power of command is vested in the President by "Article II as Commander-in-Chief. The Constitution also allows for the creation of "executive Departments" headed by "principal officers" whose opinion the President can require. This allowance in the Constitution formed the basis for creation of the "Department of Defense in 1947 by the "National Security Act. The Defense Department is headed by the "Secretary of Defense, who is a civilian and member of the "Cabinet. The Defense Secretary is second in the Armed Forces' "chain of command(with the exception of the Coast Guard, which is under the "Secretary of Homeland Security), just below the President, and serves as the principal assistant to the President in all defense-related matters.[20] Together, the President and the Secretary of Defense comprise the "National Command Authority, which by law, is the ultimate lawful source of military orders.[21]

All of the branches work together during operations and joint missions in "Unified Combatant Commands, under the authority of the Secretary of Defense with the exception of the Coast Guard. Each of the Unified Combatant Commands is headed by a Combatant Commander, a senior "commissioned officer who exercises supreme command authority per "10 U.S.C.§ 164 over all of the forces, regardless of branch, within his geographical or functional command. By statute, the chain of command flows from the President to the Secretary of Defense to each of the Combatant Commanders.[26] In practice, the Chairman of the Joint Chiefs of Staff often acts as an intermediary between the Secretary of Defense and the Combatant Commanders.

U.S. military spending from 1910 to 2007, adjusted for inflation to 2003 dollars. The large spike represents "World War II spending.

""

""

American defense spending by GDP percentage 1910 to 2007.

The United States has the "world's largest "military budget. In the fiscal year 2016, $580.3 billion in funding were enacted for the Department of Defense (DoD) and for "Overseas Contingency Operations" in the "War on Terrorism.[4] Outside of direct DoD spending, the United States spends another $218 to $262 billion each year on other defense-related programs, such as Veterans Affairs, Homeland Security, nuclear weapons maintenance, and the State Department.

By service, $146.9 billion was allocated for the Army, $168.8 billion for the Navy and Marine Corps, $161.8 billion for the Air Force and $102.8 billion for defense-wide spending.[4] By function, $138.6 billion was requested for personnel, $244.4 billion for operations and maintenance, $118.9 billion for procurement, $69.0 billion for research and development, $1.3 billion for revolving and management funds, $6.9 billion for military construction, and $1.3 billion for family housing.[4]

In FY 2009, major defense programs saw continued funding:

$4.1 billion was requested for the next-generation fighter, "F-22 Raptor, which was to roll out an additional 20 planes in 2009

$6.7 billion was requested for the "F-35 Lightning II, which is still under development, but 16 planes were slated to be built

Loren Thompson, a defense analyst with the "Lexington Institute, has blamed the "vast sums of money" squandered on cutting-edge technology projects that were then canceled on shortsighted political operatives who lack a long-term perspective in setting requirements. The result is that the number of items bought under a given program are cut. The total development costs of the program are divided over fewer platforms, making the per-unit cost seem higher and so the numbers are cut again and again in a death spiral.[27] Although the United States was the world's biggest exporter of major weapons in 2010–14, the US was also the world's eight biggest importer during the same period. US arms imports increased by 21 percent between 2005–2009 and 2010–14.[10]

Active duty U.S. military personnel from 1950 to 2003. The two peaks correspond to the "Korean War and the "Vietnam War.

The projected active duty end strength in the armed forces for FY 2017 was 1,281,900 people,[4] with an additional 801,200 people in the seven reserve components.[4] It is an all-volunteer military, but conscription through the "Selective Service System can be enacted at the President's request and Congress' approval. All males ages 18 through 25 who are living in the United States are required to register with the Selective Service for a potential future draft.

From 1776 until September 2012, a total of 40 million people have served in the United States Armed Forces.[30]

The FY 2017 DoD budget request[4] plan calls for an active duty end strength of 1,281,900, a decrease of 19,400 from the 2016 baseline as a result of decrements in the Army (15,000 fewer personnel) and Navy (4,400 fewer personnel) strength. The budget request also calls for a reserve component end strength of 801,200, a decrease of 9,800 personnel.

As in most militaries, members of the U.S. Armed Forces hold a rank, either that of "officer, "warrant officer, or "enlisted, to determine seniority and eligibility for promotion. Those who have served are known as "veterans. Rank names may be different between services, but they are matched to each other by their corresponding "paygrade.[31] Officers who hold the same rank or paygrade are distinguished by their date of rank to determine seniority, while officers who serve in certain positions of office of importance set by law, outrank all other officers in active duty of the same rank and paygrade, regardless of their date of rank.[32] Currently, only one in four persons in the United States of the proper age meet the moral, academic and physical standards for military service.[33]

These numbers do not take into account the use of Private Military and Private Security Companies (PSCs). Quarterly PSC census reports are available for "United States Central Command (USCENTCOM)'s area of operations—i.e., Iraq and Afghanistan.[39] As of March 2011, there were 18,971 private security contractor (PSC) personnel in Afghanistan working for DoD; in Iraq, there were 9,207 PSC personnel, down from a high of 15,279 in June 2009.[40] As of October 2012, in Afghanistan, there were 18,914 PSC personnel working for DoD; in Iraq, there were 2,116 PSC personnel.[41] The total number of DoD contractors in Iraq and Afghanistan was more than 137,400; reported PSCs were only a part of the number.

As of 31 December 2010, U.S. Armed Forces troops were stationed in 150 countries; the number of non-contingent deployments per country ranges from 1 in "Suriname to over 50,000 in Germany.[42] Some of the largest deployments are: 103,700 in "Afghanistan, 52,440 in "Germany(see "list), 35,688 in Japan ("USFJ), 28,500 in "South Korea ("USFK), 9,660 in "Italy, and 9,015 in the United Kingdom. These numbers change frequently due to the regular recall and deployment of units.

As of 31 December 2009, a total of 1,137,568 personnel were on active duty within the United States and its "territories (including 84,461 afloat).[43] The vast majority (941,629 personnel) were stationed at bases within the "contiguous United States. There were an additional 37,245 in "Hawaii and 20,450 in "Alaska; 84,461 were at sea, 2,972 in "Guam, and 179 in "Puerto Rico.

Prospective service members are often "recruited from high school or college, the target age ranges being 18–35 in the Army, 18–28 in the Marine Corps, 18–34 in the Navy, 18–39 in the Air Force, and 18–27 (up to age 32 if qualified for attending guaranteed "A" school) in the Coast Guard. With the permission of a parent or guardian, applicants can enlist at age 17 and participate in the "Delayed Entry Program (DEP), in which the applicant is given the opportunity to participate in locally sponsored military activities, which can range from sports to competitions led by recruiters or other military liaisons (each recruiting station's DEP varies).

After enlistment, new recruits undergo "basic training (also known as "boot camp" in the Marine Corps, Navy and Coast Guard), followed by schooling in their primary "Military Occupational Specialty (MOS), "rating, "Air Force Specialty Code (AFSC) at any of the numerous training facilities around the United States. Each branch conducts basic training differently. The Marine Corps send all non-infantry MOS's to an infantry skills course known as "Marine Combat Training prior to their technical schools. Air Force Basic Military Training graduates attend Technical Training and are awarded their Air Force Specialty Code (AFSC) at the apprentice (3) skill level. All Army recruits undergo "Basic Combat Training (BCT), followed by "Advanced Individual Training (AIT), with the exceptions of cavalry scouts, infantry, armor, combat engineers, and military police recruits who go to One Station Unit Training (OSUT), which combines BCT and AIT. The Navy sends its recruits to Recruit Training and then to "A" schools to earn a rating. The Coast Guard's recruits attend basic training and follow with an "A" school to earn a "rating.

Initially, recruits without higher education or college degrees will hold the pay grade of E-1, and will be elevated to E-2 usually soon after basic training. Different services have different incentive programs for enlistees, such as higher initial ranks for college credit, being an "Eagle Scout, and referring friends who go on to enlist as well. Participation in DEP is one way recruits can achieve rank before their departure to basic training.

There are several different authorized pay grade advancement requirements in each junior-enlisted rank category (E-1 to E-3), which differ by service. Enlistees in the Army can attain the initial pay grade of E-4 (specialist) with a four-year degree, but the highest initial pay grade is usually E-3 (members of the Army Band program can expect to enter service at the grade of E-4). Promotion through the junior enlisted ranks occurs after serving for a specified number of years (which, however, can be waived by the soldier's chain of command), a specified level of technical proficiency, or maintenance of good conduct. Promotion can be denied with reason.

With very few exceptions, becoming a "non-commissioned officer (NCO) or "petty officer in the U.S. Armed Forces is accomplished by progression through the lower enlisted ranks. However, unlike promotion through the lower enlisted tier, promotion to NCO is generally competitive. NCO ranks begin at E-4 or E-5, depending upon service, and are generally attained between three and six years of service. Junior NCOs function as first-line supervisors and squad leaders, training the junior enlisted in their duties and guiding their career advancement.

While considered part of the non-commissioned officer corps by law, senior non-commissioned officers (SNCOs) referred to as "chief petty officers in the Navy and Coast Guard, or staff non-commissioned officers in the Marine Corps, perform duties more focused on leadership rather than technical expertise. Promotion to the SNCO ranks, E-7 through E-9 (E-6 through E-9 in the Marine Corps) is highly competitive. Personnel totals at the pay grades of E-8 and E-9 are limited by federal law to 2.5 percent and 1 percent of a service's enlisted force, respectively. SNCOs act as leaders of small units and as staff. Some SNCOs manage programs at headquarters level and a select few wield responsibility at the highest levels of the military structure. Most unit commanders have a SNCO as an enlisted advisor. All SNCOs are expected to mentor junior commissioned officers as well as the enlisted in their duty sections. The typical enlistee can expect to attain SNCO rank after 10 to 16 years of service.

Each of the five services employs a single "Senior Enlisted Advisor at departmental level. This individual is the highest ranking enlisted member within that respective service and functions as the chief advisor to the service secretary, service chief, and Congress on matters concerning the enlisted force. These individuals carry responsibilities and protocol requirements equivalent to "three-star "general or "flag officers. They are as follows:

Additionally, all services except for the Air Force have an active "warrant officer corps. Above the rank of warrant Officer One, these officers may also be commissioned, but usually serve in a more technical and specialized role within units. More recently though they can also serve in more traditional leadership roles associated with the more recognizable officer corps. With one notable exception (Army helicopter and "fixed-wing pilots), these officers ordinarily have already been in the military often serving in senior NCO positions in the field in which they later serve as a warrant officer as a technical expert. Most Army pilots have served some enlisted time. It is also possible to enlist, complete basic training, go directly to the "Warrant Officer Candidate School at "Fort Rucker, Alabama, and then on to "flight school.

Warrant officers in the U.S. military garner the same customs and courtesies as commissioned officers. They may attend the officer's club, receive a command and are saluted by junior warrant officers and all enlisted service members.

The Air Force ceased to grant warrants in 1959 when the enlisted grades of E-8 and E-9 were created. Most non-flying duties performed by warrant officers in other services are instead performed by senior NCOs in the Air Force.

"Direct commission: civilians who have special skills that are critical to sustaining military operations and supporting troops may receive direct commissions. These officers occupy leadership positions in law, medicine, dentistry, pharmacy, intelligence, supply-logistics-transportation, engineering, public affairs, chaplain, "oceanography, and others.

"Battlefield commission: Under certain conditions, enlisted personnel who have skills that separate them from their peers can become officers by direct commissioning of a commander so authorized to grant them. This type of commission is rarely granted and is reserved only for the most exceptional enlisted personnel; it is done on an ad hoc basis, typically only in wartime. No direct battlefield commissions have been awarded since the "Vietnam War. The Navy and Air Force do not employ this commissioning path.

"Limited Duty Officer: Due to the highly technical nature of some officer "billets, the Marine Corps, Navy, and Coast Guard employ a system of promoting proven senior enlisted members to the ranks of commissioned officers. They fill a need that is similar to, but distinct from that filled by warrant officers (to the point where their accession is through the same school). While warrant officers remain technical experts, LDOs take on the role of a generalist, like that of officers commissioned through more traditional sources. LDOs are limited, not by their authority, but by the types of billets they are allowed to fill. However, in recent times, they have come to be used more and more like their more-traditional counterparts.

Officers receive a commission assigning them to the officer corps from the President with the Senate's "consent. To accept this commission, all officers must take an "oath of office.

Through their careers, officers usually will receive further training at one or a number of the many "staff colleges.

"Company grade officers in pay grades O-1 through O-3 (known as "junior" officers in the Navy and Coast Guard) function as leaders of smaller units or sections of a unit, typically with an experienced SNCO (or CPO in the Navy and Coast Guard) assistant and mentor.

"Field grade officers in pay grades O-4 through O-6 (known as "senior" officers in the Navy and Coast Guard) lead significantly larger and more complex operations, with gradually more competitive promotion requirements.

"General officers, (known as "flag officers in the Navy and Coast Guard) serve at the highest levels and oversee major portions of the military mission.

These are ranks of the highest honor and responsibility in the U.S. Armed Forces, but they are almost never given during peacetime and only a very small number of officers during wartime have held a five-star rank:

No corresponding rank exists for the Marine Corps or the Coast Guard. As with three- and four-star ranks, Congress is the approving authority for a five-star rank confirmation.

The rank of "General of the Armies is considered senior to General of the Army, but was never held by active duty officers at the same time as persons who held the rank of General of the Army. It has been held by two people: "John J. Pershing who received the rank in 1919 after World War I, and "George Washington who received it posthumously in 1976 as part of the "American Bicentennial celebrations. Pershing, appointed to General of the Armies in active duty status for life, was still alive at the time of the first five-star appointments during World War II, and was thereby acknowledged as superior in grade by seniority to any World War II–era Generals of the Army. George Washington's appointment by Public Law 94-479 to General of the Armies of the United States was established by law as having "rank and precedence over all other grades of the Army, past or present", making him not only superior to Pershing, but superior to any grade in the Army in perpetuity.

In the Navy, the rank of "Admiral of the Navy theoretically corresponds to that of General of the Armies, though it was never held by active-duty officers at the same time as persons who held the rank of Fleet Admiral. "George Dewey is the only person to have ever held this rank. After the establishment of the rank of Fleet Admiral in 1944, the Department of the Navy specified that the rank of Fleet Admiral was to be junior to the rank of Admiral of the Navy. However, since Dewey died in 1917 before the establishment of the rank of Fleet Admiral, the "six-star rank has not been totally confirmed.

After World War II, demobilization led to the vast majority of serving women being returned to civilian life. Law 625, "The Women's Armed Services Act of 1948, was signed by "President Truman, allowing women to serve in the U.S. Armed Forces in fully integrated units during peace time, with only the WAC remaining a separate female unit. During the "Korean War of 1950–1953 many women served in the "Mobile Army Surgical Hospitals, with women serving in Korea numbering 120,000 during the conflict. During the "Vietnam War, 600 women served in the country as part of the Air Force, along with 500 members of the WAC, and over 6,000 medical personnel and support staff. The "Ordnance Corps began accepting female missile technicians in 1974,[45] and female crewmembers and officers were accepted into "Field Artillery missile units.[46][47]

In 1974, the first six women naval aviators earned their wings as "Navy pilots. The Congressionally mandated prohibition on women in combat places limitations on the pilots' advancement,[48] but at least two retired as captains.[49] In 1989, Capt Linda L. Bray, 29, became the first woman to command American soldiers in battle, during the "invasion of Panama. The 1991 "Gulf War proved to be the pivotal time for the role of women in the U.S. Armed Forces to come to the attention of the world media. There are many reports of women engaging enemy forces during the conflict.[50]

In the 2000s, women can serve on U.S. combat ships, including in command roles. They are permitted to serve on submarines.[51] Women can fly military aircraft and make up 2% of all pilots in the U.S. Military. In 2003, Major "Kim Campbell was awarded the "Distinguished Flying Cross for landing her combat damaged "A-10 Thunderbolt II with no hydraulic control and only one functional engine after being struck by hostile fire over "Baghdad.

On 3 December 2015, United States of America Defense Secretary, Ashton Carter, announced that all military combat jobs would become available to women.[52] This gave women access to the roughly 10% of military jobs which were previously closed off due to their combat nature.[53] The decision gave military services until January 2016 to seek exceptions to the rule if they believe that certain jobs, such as machine gunner's, should be restricted to men only.[54] These restrictions were due in part to prior studies which stated that mixed gender units are less capable in combat.[55] Physical requirements for all jobs remained unchanged, though.[55] Many women believe this will allow for them to improve their positions in the military since most high-ranking officers start in combat positions. Since women are now available to work in any position in the military, female entry into the draft has been proposed.[56]

Sergeant "Leigh Ann Hester became the first woman to receive the Silver Star, the third-highest US decoration for valor, for direct participation in combat. In Afghanistan, Monica Lin Brown was presented the Silver Star for shielding wounded soldiers with her body.[57] In March 2012, the U.S. military had two women, "Ann E. Dunwoody and "Janet C. Wolfenbarger, with the rank of four-star general.[58][59] In 2016, Air Force General "Lori Robinson became the first female officer to command a major "Unified Combatant Command ("USNORTHCOM) in the history of the United States Armed Forces.[60]

Under current Department of Defense regulation, the various components of the U.S. Armed Forces have a set order of seniority. Examples of the use of this system include the display of service flags, placement of Soldiers, Marines, Sailors, Airmen, and Coast Guardsmen in formation, etc. When the Coast Guard shall operate as part of the Department of the Navy, United States Coast Guard Academy cadets, the United States Coast Guard, and the Coast Guard Reserve shall take precedence, respectively, after United States Naval Academy midshipmen; the United States Navy; and Navy Reserve.[61]

Note: While the U.S. Navy is older than the Marine Corps,[62] the Marine Corps takes precedence due to previous inconsistencies in the Navy's birth date. The Marine Corps has recognized its observed birth date on a more consistent basis. The "Second Continental Congress is considered to have established the Navy on 13 October 1775 by authorizing the purchase of ships, but did not actually pass the ""Rules for the Regulation of the Navy of the United Colonies" until 27 November 1775.[63] The Marine Corps was established by act of said Congress on 10 November 1775. The Navy did not officially recognize 13 October 1775 as its birth date until 1972, when then–"Chief of Naval Operations Admiral "Elmo Zumwalt authorized it to be observed as such.[62]

^The United States Coast Guard has both military and law enforcement functions. "Title 14 of the United States Code provides that "The Coast Guard as established 28 January 1915, shall be a military service and a branch of the armed forces of the United States at all times." Coast Guard units, or ships of its predecessor service, the Revenue Cutter Service, have seen combat in every war and armed conflict of the United States since 1790, including the Iraq War.